The invention relates to exhaust manifold devices.
In U.S. Pat. No. 3,871,175, a secondary air supply system is described that supplies air to an exhaust manifold to provide sufficient air to oxidise any unburnt exhaust gases at lower engine speeds.
The invention relates more particularly to devices that are arranged to automatically allow air to enter the exhaust manifold to prevent inter alia exhaust gases being sucked into engine cylinders during the normal operation of the engine. Such devices or aspirators have been disclosed already in, for example, U.S. Pat. No. 3,455,106 and European Patent 0041831. Devices so far proposed comprise relatively complicated mechanical arrangements and do not operate efficiency at higher engine speeds or at a variety of engine speeds.
It is an object of the invention to overcome or at least reduce these problems.
According to the invention there is provided an aspirator for allowing air automatically to selectively enter an engine exhaust manifold during operation of an internal combustion engine to inhibit exhaust gases being drawn back into the cylinders via exhaust valves, the aspirator comprising an adapter formed by a hollow body that extends to a port fitted in communication with the manifold, a first one way valve fitted to the adapter that prevents gases leaving the manifold through the port when the pressure inside the manifold is greater than the pressure at the first valve, and means for supplying air to a second one way valve at different pressures, above atmospheric pressure, that increase with increases of speed of the engine, in which the second one way valve is connected by a passageway to the first valve forming an intermediate expansion chamber, the second one way valve being arranged to allow air to enter the passageway whenever the pressure inside the passageway is less than the pressure at the second valve, including means for supplying electrical signals synchronised with exhaust valve operation to open the first one way valve.
The port is preferably formed in a tube that extends somewhat in to the manifold beyond its inner surface.
The one way valves may each comprise a needle valve.
The position of the second one way valve may be manually adjustable to vary the differential pressure at which the second valve opens and closes.
The air may be supplied to the second one way valve by an air ram having an inlet exposed forwardly in a vehicle in which the engine is mounted so as to provide air at a pressure corresponding to the forward speed of the vehicle.
The air may also or alternatively be supplied by an air pump, and the air pump may form part of a turbo charger for the engine.
The means for supplying electrical signals may comprise an engine ignition unit.
The means for supplying synchronised electrical signals may comprise a pressure sensitive switch mounted in communication with the exhaust manifold, and include a normally-open electrical switch arranged to close in accordance with pressure in the manifold reducing to a predetermined pressure.
The means for supplying synchronised electrical signals may include markers mounted on a flywheel of the engine.